1. FIELD OF THE INVENTION
The present invention relates to webbing lock devices for use in a seatbelt system for restraining and protecting an occupant in an emergency of a vehicle, and more particularly to a webbing lock device for instantly preventing an occupant restraining webbing from moving in the longitudinal direction so as to reliably restrain the occupant.
2. DESCRIPTION OF THE PRIOR ART
Heretofore, there have been proposed automatically fastening type seatbelt systems for automatically fastening a restraining webbing to an occupant of a vehicle after he is seated. There have also been proposed webbing lock devices used in said automatically fastening type seatbelt systems for making it possible to freely wind the webbing out of a takeup shaft during normal running condition of the vehicle and for suddenly preventing the webbing from being wound out in an emergency of the vehicle. Said webbing lock device is of such an arrangement that a portion of the webbing between the takeup shaft and the portion of the webbing fastened to the occupant is clamped between a pair of lock members to prevent the webbing from moving in the longitudinal direction, so that the occupant can be positively restrained. The lock members of said lock device have clamping surfaces being wave-shaped in cross section, whereby frictions generated between the lock members and the webbing are increased, so that the webbing can be reliably locked. During an emergency of the vehicle, a pair of wave-shaped surfaces are adapted to bend the intermediate portion of the webbing into a wave-shape, whereby the frictions generated between the webbing and the lock members are increased.
However, because the lock members are subjected to a high tension of the webbing during clamping the webbing therebetween, it is necessary to form the lock members into shapes capable of maintaining a predetermined mechanical strength, thus causing the production efficiency to be decreased to a considerable extent. Furthermore, the lock members using the wave-shaped surfaces are comparatively large-sized and heavy in weight, thus preventing the lock device from being rendered compact and light weight.
Additionally, when the clamping surfaces of the lock members are formed flat, the tension of the webbing is sharply changed in the clamping portions of the lock members during an emergency, thereby presenting the disadvantage of the webbing being ruptured.